The loss of skeletal muscle mass with aging (sarcopenia) is important to public health due to its effects on the functional capacity of older adults. The rhesus monkey provides an outstanding model to study sarcopenia and the effect of dietary restriction (DR) on its progression in primates. We hypothesize that DR induces an altered state of mitochondrial energy metabolism that is central to the retardation of aging, and that this "metabolic shift" is responsible for slowing the rate of sarcopenia in DR animals. Specific Aim 1: To generate transcriptional and proteomic profiles of the effects of age and DR on skeletal muscle. This is a longitudinal study on vastus lateralis (VL) biopsies obtained from Group 1 monkeys in 1994 and year one of the study. Affymetrix human microarray data will be mined to probe functional groups of genes central to energy metabolism with a focus on genes involved in mitochondrial function. Comparative proteomic analysis of mitochondria from the same biopsies and Group 2 animals, using 2D electrophoresis and mass spectrometry, will further define mitochondrial status. Western blot analysis will confirm the results of the microarray work and examine the effect of age and DR on specific proteins involved in metabolic regulation and cell signaling. Specific Aim 2: To identify critical ages at which phenotypes of sarcopenia emerge in the rhesus monkey and to define the effect of DR on the progression of muscle changes with age. Analyses of changes in quadriceps muscles from male and female Wisconsin National Primate Research Center (WNPRC) colony and PPGsupported monkeys collected at necropsy, as well as biopsy samples from control and DR monkeys, combined with longitudinal DXA and MRI muscle mass estimations from live monkeys over time, will define specific ages at which muscle mass loss, muscle fiber loss, muscle fiber atrophy and mitochondrial enzyme abnormalities present in aging rhesus monkeys. Specific Aim 3: To quantitate mtDNA deletion mutations and abundance of specific mRNAs in single microdissected sections of muscle fibers. Laser capture microdissection will be used to select, from DR and control monkeys, single vastus lateralis muscle fibers exhibiting ETS normal and ETS abnormal phenotypes. The abundance of WT and mtDNA deletion mutations as well as the levels of selected mRNAs, the abundance of which change with age and/or diet (identified in Aim 1), will be quantified.